Cross-linking silicone elastomers, method for the production thereof, and use of the cross-linkable masses

ABSTRACT

Addition crosslinkable organopolysiloxane compositions employ specific rhodium catalysts. The compositions exhibit storage stability and crosslink effectively to provide highly transparent and colorless organopolysiloxane elastomers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to silicone elastomers which crosslink by specialrhodium compounds, a process for preparation thereof and also the use ofthe crosslinkable compositions.

2. Description of the Related Art

Silicone elastomers are customarily produced by crosslinking withplatinum or platinum compounds.

Disadvantages of silicones which are crosslinked with platinum orplatinum compounds are the yellow and/or brown color of the crosslinkedsilicones which are visible, in particular in the case of high siliconecontents by volume. The discoloration is caused by the platinum which,at the end of the crosslinking, is present as a platinum colloid asdescribed in the literature, J. Am. Chem. Soc. 108 (1986) 7228ff. Inaddition, in the case of many platinum-crosslinked silicones, thetransparency is decreased and the silicone elastomers are as a resultnot transparent, but cloudy, which is termed translucent. The platinumcatalysts have the further disadvantage that silicone rubbers comprisingthem have only a restricted processing time after the essentialconstituents are mixed, because after the individual components aremixed the platinum crosslinking begins straight away at roomtemperature. Although the processing time of the compositions may beincreased by incorporating a substance inhibiting the activity of theplatinum catalyst (these are generally termed inhibitors), the curingrate of the composition is in turn decreased as a result.

In a few cases, rhodium catalysts are also described for crosslinkingsilicone elastomers. U.S. Pat. No. 4,262,107 describes silicone rubbercompositions which comprise silanol-endstopped polydiorganosiloxanes,silicone hydrides and rhodium catalysts. However in the case of thissystem, a hydrosilylation reaction does not take place, but, instead, acondensation reaction of ≡Si—OH and ≡Si—H to form ≡—Si—O—Si≡, withelimination of hydrogen. This system may be suitable for producingcoatings, but it is not suitable for producing molded parts because ofthe hydrogen formation. DE 24 29 772 describes silicone compositionswhich consist of a vinyl group-containing polyorganosiloxane, apolyorganosiloxane containing silicon-bonded hydrogen atoms, and arhodium catalyst. Rhodium catalysts used are complexes of the formulaRhX₃(SR₂)₃ or Rh₂(CO)₄X₂, where X is halogen and R in each case isalkyl, aryl, aralkyl or alkylaryl. The resultant silicone compositionshave, as advantages, long processing times after all essentialconstituents have been mixed together at room temperature, even withoutinhibitors, and good crosslinking characteristics at elevatedtemperatures. A great disadvantage when RhX₃(SR₂)₃, which is describedas preferred in DE 24 29 772, is used is the thioethers (SR₂) which areused as ligands. These thioethers are not incorporated by crosslinking,are highly malodorous and are extremely toxic. Furthermore, thesethioethers, in some cases, due to the sulfur group, lead to theresultant silicone elastomers having a yellow color. Rh₂(CO)₄X₂ also hasserious disadvantages. The most serious is certainly the fact that thecompound is not stable per se in moist air and gradually decomposes.Inorg. Synth. 8 (1966), 211 ff. The rhodium complex in the siliconecomposition therefore is already beginning to decompose after the latterhas been prepared. If it is considered that it can take several monthsuntil the silicone composition is processed at the client's premises, itbecomes clear that the rhodium complex at this time is alreadydecomposed and is no longer present in its original form, which leads tothe fact that the silicone composition either no longer crosslinks atall or has completely unexpected and unwanted crosslinkingcharacteristics.

SUMMARY OF THE INVENTION

It was therefore an object to provide silicone compositions whichovercome the disadvantages of the prior art, in particular enable longprocessing times at room temperature without inhibitor, which curerapidly at elevated temperatures, and whose vulcanized form exhibitsextremely high transparency without yellow or brown coloring.

We have now surprisingly found that the problems can be solved ifspecial rhodium compounds are used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention therefore relates to organopolysiloxanecompositions which cure via at least one rhodium compound and comprise

-   (A) compounds which have radicals containing aliphatic carbon-carbon    multiple bonds,-   (B) organopolysiloxanes containing Si-bonded hydrogen atoms or,    instead of (A) and (B)-   (C) organopolysiloxanes which have SiC-bonded radicals containing    aliphatic carbon-carbon multiple bonds and Si-bonded hydrogen atoms,    and-   (D) a rhodium catalyst, at least one being selected from the group    consisting of-   compounds of the formula    [(R²—C(═O)—O—)₂Rh]₂  (III),    L(X)Rh(PR³ ₃)_(s)  (VI)-   or

-   where-   R² can be identical or different and is a hydrogen atom, or    monovalent unsubstituted or substituted hydrocarbon radicals having    from 1 to 24 carbon atoms,-   R³ can be identical or different and is hydrogen, —OR⁴ or monovalent    unsubstituted or substituted hydrocarbon radicals having from 1 to    24 carbon atoms,-   R⁴ can be identical or different and is a hydrogen atom, or a    monovalent unsubstituted or substituted hydrocarbon radical having    from 1 to 20 carbon atoms,-   X can be identical or different and is halogen or hydrogen,-   L can be identical or different and is CO, acetylacetonate (as    O,O-chelate), 0.5 cyclooctadiene, 0.5 norbornadiene or P(R³)₃ and-   S is 2 or 3.

Where substituted radicals are involved, the substituents are preferablyhalogen atoms, such as F, Cl, Br and I, cyano radicals, heteroatoms,such as O, S, N and P, and also groups —OR⁴, where R⁴ has the meaningspecified above.

The inventive compositions can be single-component organopolysiloxanecompositions, and also two-component organopolysiloxane compositions. Inthe latter case, the two components of the inventive compositions cancomprise all constituents in any desired combination, generally with theproviso that a component does not simultaneously comprise siloxanescontaining an aliphatic multiple bond, siloxanes having Si-bondedhydrogen and catalyst, that is to say does not essentiallysimultaneously comprise the constituents (A), (B) and (D), or (C) and(D). Particular preference is given here to one component comprising theconstituents (A), (B) or only (C), and the second component comprising(A) and (D).

The compounds (A) and (B) or (C) used in the inventive compositions areselected as is known so that crosslinking is possible. Thus, for examplecompound (A) has at least two aliphatically unsaturated radicals andsiloxane (B) at least three Si-bonded hydrogen atoms, or compound (A)has at least three aliphatically unsaturated radicals and siloxane (B)at least two Si-bonded hydrogen atoms, or else, instead of compound (A)and (B), siloxane (C), which has aliphatically unsaturated radicals andSi-bonded hydrogen atoms in the abovementioned ratios, is used.

Preferably, the inventive silicone compositions comprise, as constituent(A), an aliphatically unsaturated organosilicon compound, in which caseall aliphatically unsaturated organosilicon compounds previously used inaddition-crosslinking compositions can be used, and also, for example,silicone block copolymers containing urea segments, silicone blockcopolymers containing amide segments and/or imide segments and/orester-amide segments and/or polystyrene segments and/or silarylenesegments and/or carborane segments and silicone graft copolymerscontaining ether groups.

As organosilicon compound (A) having SiC-bonded radicals containingaliphatic carbon-carbon multiple bonds, use is preferably made of linearor branched organopolysiloxanes composed of units of the formulaR_(a)R¹ _(b)SiO_((4−a−b)/2)  (I),where

-   R can be identical or different and is an organic radical free from    aliphatic carbon-carbon multiple bonds,-   R¹ can be identical or different and is a monovalent unsubstituted    or substituted SiC-bonded hydrocarbon radical containing an    aliphatic carbon-carbon multiple bond,-   a is 0, 1, 2 or 3 and-   b is 0, 1 or 2-   with the proviso that the sum a+b is less than or equal to 3 and on    average at least 2 radicals R¹ are present per molecule.

Examples of radicals R are alkyl radicals, such as the methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl,neopentyl, tert-pentyl radical, hexyl radicals, such as the n-hexylradical, heptyl radicals, such as the n-heptyl radical, octyl radicals,such as the n-octyl radical and isooctyl radicals, such as the2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonylradical, decyl radicals, such as the n-decyl radical, dodecyl radicals,such as the n-dodecyl radical, and octadecyl radicals, such as then-octadecyl radical, cycloalkyl radicals, such as cyclopentyl,cyclohexyl, cycloheptyl and methylcyclohexyl radicals, aryl radicals,such as the phenyl, naphthyl, anthryl and phenanthryl radical, alkarylradicals such as o-, m-, p-tolyl radicals, xylyl radicals andethylphenyl radicals, and aralkyl radicals, such as the benzyl radical,the α- and β-phenylethyl radical.

Examples of substituted radicals R are haloalkyl radicals, such as the3,3,3-trifluoro-n-propyl radical, the 2,2,2,2′,2′,2′-hexafluoroisopropylradical and the heptafluoroisopropyl radical, haloaryl radicals, such asthe o-, m- and p-chlorophenyl radicals.

Preferably, the radical R is a monovalent, SiC-bonded, unsubstituted orsubstituted hydrocarbon radical which is free from aliphaticcarbon-carbon multiple bonds and contains from 1 to 18 carbon atoms,particularly preferably a monovalent SiC-bonded hydrocarbon radicalwhich is free from aliphatic carbon-carbon multiple bonds and containsfrom 1 to 6 carbon atoms, in particular the methyl or phenyl radical.

The radical R¹ can be any group accessible to an addition reaction(hydrosilylation) with an SiH-functional compound.

Where the radical R¹ is an SiC-bonded substituted hydrocarbon radical,the preferred substituents are halogen atoms, cyano radicals and —OR⁴,where R⁴ has the meaning specified above.

Preferably, radical R¹ is alkenyl and alkynyl groups containing from 2to 16 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl,5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl,cyclopentadienyl, cyclohexenyl, vinylcyclohexylethyl,divinylcyclohexylethyl, norbornenyl, vinylphenyl and styryl radicals,vinyl, alkynyl, allyl and hexenyl radicals being particularly preferred.

The molecular weight of the constituent (A) can vary within broadlimits, for instance between 10² and 10⁶ g/mol. Thus, the constituent(A) can be, for example, a relatively low-molecular-weight alkenylfunctional oligosiloxane, such as 1,2-divinyltetramethyldisiloxane, butalso a high-polymer polydimethylsiloxane having chain-position orterminal Si-bonded vinyl groups, for example having a molecular weightof 10⁵ g/mol (number average determined by NMR). The structure of themolecules forming the constituent (A) is also not fixed; in particularthe structure of a higher-molecular-weight, that is to say oligomeric orpolymeric siloxane, can be linear, cyclic, branched or else resin-like,network-like. Linear and cyclic polysiloxanes are preferably composed ofunits of the formulae R₃SiO_(1/2), R¹R₂SiO_(1/2), R¹RSiO_(2/2) andR₂SiO_(2/2), where R and R¹ have the meaning specified above. Branchedand network-like polysiloxanes additionally contain trifunctional and/ortetrafunctional units, those of the formulae RSiO_(3/2), R¹SiO_(3/2) andSiO_(4/2) being preferred. Of course, mixtures of different siloxanessatisfying the criteria of constituent (A) can also be used.

Particular preference is given to using vinyl functional, essentiallylinear, polydiorganosiloxanes having a viscosity of from 0.01 to 500,000Pa·s, particularly preferably from 0.1 to 100,000 Pa·s, in each case at25° C., as component (A)

As organosilicon compound (B), use can be made of allhydrogen-functional organosilicon compounds having a viscosity of from 1to 100,000 mPa·s, preferably from 10 to 10,000 mPa·s, particularlypreferably from 50 to 1000 mPa·s, in each case at 25° C., whichcompounds have also previously been used in addition-crosslinkablecompositions.

As organopolysiloxanes (B) which have Si-bonded hydrogen atoms, use ispreferably made of linear, cyclic or branched organopolysiloxanescomposed of units of the formulaR_(c)H_(d)SiO_((4−c−d)/2)  (II),

-   where-   R can be identical or different and has the meaning specified above,-   c is 0, 1, 2 or 3 and-   d is 0, 1 or 2,    with the proviso that the sum of c+d is less than or equal to 3 and    on average at least two Si-bonded hydrogen atoms are present per    molecule.

Preferably, the inventively used organopolysiloxane (B) containsSi-bonded hydrogen in the range from 0.04 to 1.7 percent by weight,based on the total weight of the organopolysiloxane (B).

The molecular weight of the constituent (B) can likewise vary withinbroad limits, for instance between 10² and 10⁶ g/mol. Thus, theconstituent (B) can be, for example, a relatively low-molecular-weightSiH-functional oligosiloxane, such as tetramethyldisiloxane, but also ahigh-polymer polydimethylsiloxane containing chain-position or terminalSiH groups, or an SiH-group-containing silicone resin. The structure ofthe molecules forming the constituent (B) is also not fixed; inparticular the structure of a higher-molecular-weight, that is to sayoligomeric or polymeric SiH-containing siloxane can be linear, cyclic,branched or else resin-like, network-like. Linear and cyclicpolysiloxanes are preferably composed of units of the formulaeR₃SiO_(1/2), HR₂SiO_(1/2), HRSiO_(2/2) and R₂SiO_(2/2), where R has themeaning specified above. Branched and network-like polysiloxanesadditionally contain trifunctional and/or tetrafunctional units, thoseof the formulae RSiO_(3/2), HSiO_(3/2) and SiO_(4/2) being preferred. Ofcourse, mixtures of different siloxanes meeting the criteria of theconstituent (B) can also be used. In particular, the molecules formingthe constituent (B) can, in addition to the obligatory SiH groups, whereappropriate at the same time also contain aliphatically unsaturatedgroups. Particular preference is given to the use oflow-molecular-weight SiH-functional compounds, such astetrakis(dimethylsiloxy)silane and tetramethylcyclotetrasiloxane, andalso of higher-molecular-weight, SiH-containing siloxanes, such aspoly(hydrogenmethyl)siloxane and poly(dimethylhydrogenmethyl)siloxanehaving a viscosity at 25° C. from 10 to 10,000 mPa·s, or analogousSiH-containing compounds in which a portion of the methyl groups isreplaced by 3,3,3-trifluoropropyl or phenyl groups.

Constituent (B) is preferably present in the inventive crosslinkablesilicone total compositions in an amount such that the molar ratio ofSiH groups to aliphatically unsaturated groups is from 0.1 to 20,particularly preferably between 0.8 and 4.0.

The inventively used components (A) and (B) are commerciallyconventional products or can be prepared by processes customary inchemistry.

Instead of component (A) and (B), the invention compositions cancomprise organopolysiloxanes (C) which contain aliphatic carbon-carbonmultiple bonds and Si-bonded hydrogen atoms; this is not preferred,however.

If siloxanes (C) are used, these are preferably those composed of unitsof the formulaeR_(g)SiO_(4-g/2), R_(h)R¹SiO_(3-h/2) and R_(i)HSiO_(3-i/2,)

-   where R and R¹ have the meaning specified therefor above,-   g is 0, 1, 2 or 3,-   h is 0, 1 or 2 and-   i is 0, 1 or 2,-   with the proviso that, per molecule, at least 2 radicals R¹ and at    least 2 Si-bonded hydrogen atoms are present.

Examples of organopolysiloxanes (C) are those composed of SiO_(4/2),R₃SiO_(1/2), R₂R¹SiO_(1/2) and R₂HSiO_(1/2) units, what are termed MQresins where these resins can additionally contain RSiO_(3/2) and R₂SiOunits, and also linear organopolysiloxanes essentially consisting ofR₂R¹SiO_(1/2), R₂SiO and RHSiO units with R and R¹ being identical tothe meaning specified above.

The organopolysiloxanes (C) preferably have a mean viscosity of from0.01 to 500,000 Pa·s, particularly preferably from 0.1 to 100,000 Pa·s,in each case at 25° C.

Organopolysiloxanes (C) can be prepared by methods customary inchemistry.

Examples of R² are alkyl radicals, such as the methyl, ethyl, n-propyl,isopropyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl, n-pentyl,isopentyl, neopentyl, tert-pentyl radical, hexyl radicals, such as then-hexyl radical, heptyl radicals, such as the n-heptyl radical, octylradicals, such as the n-octyl radical and isooctyl radicals, such as the2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonylradical, decyl radicals, such as the n-decyl radical, cycloalkylradicals, such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptylradicals and methylcyclohexyl radicals, unsaturated radicals, such asthe allyl, 5-hexenyl, 7-octenyl, cyclohexenyl and styryl radical, arylradicals, such as phenyl radicals, o-, m- p-tolyl radicals, xylylradicals and ethylphenyl radicals and aralkyl radicals, such as thebenzyl radical and the α- and β-phenylethyl radical. particularlypreferably, R² is hydrogen, methyl and octyl radicals.

Examples of R³ are alkyl radicals, such as the methyl, ethyl, n-propyl,isopropyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl, n-pentyl,isopentyl, neopentyl, tert-pentyl radical, hexyl radicals, such as then-hexyl radical, heptyl radicals, such as the n-heptyl radical, octylradicals, such as the n-octyl radical and isooctyl radicals, such as the2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonylradical, decyl radicals, such as the n-decyl radical, cycloalkylradicals, such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptylradicals and methylcyclohexyl radicals, unsaturated radicals, such asthe allyl, 5-hexenyl, 7-octenyl, cyclohexenyl and styryl radical, arylradicals, such as phenyl radicals, o-, m-, p-tolyl radicals, xylylradicals and ethylphenyl radicals, aralkyl radicals, such as the benzylradical and the α- and α-phenylethyl radical, and also radicals of theformula —C(R¹)═CR¹ ₂; further examples of R³ are —OR⁴ radicals, such ashydroxyl, methoxy, ethoxy, isopropoxy, butoxy and phenoxy radicals.

Examples of halogenated radicals R³ are haloalkyl radicals, such as the3,3,3-trifluoro-n-propyl radical, the 2,2,2,2′,2′,2′-hexafluoroisopropylradical, the heptafluoroisopropyl radical and haloaryl radicals, such asthe o-, m-, and p-chlorophenyl radical.

Preferably, radical R³ is a hydrogen atom, methyl, butyl, phenyl,hydroxyl, methoxy, phenoxy, octyloxy radicals and hydrocarbon radicalscontaining from 1 to 8 carbon atoms, hydrogen atom, phenoxy radical,methyl, butyl and phenyl radical being particularly preferred.

Examples of radical R⁴ are the radicals specified for radical R³.

Preferably, R⁴ is hydrogen atom, alkyl radicals and aryl radicals,hydrogen atom, the methyl, the phenyl and the ethyl radical beingparticularly preferred.

The inventively used rhodium compounds are known to those skilled in theart and some can be obtained commercially, or can be prepared by knownpreparation instructions.

The inventively used rhodium catalyst (D) is preferably

-   (acetylacetonato)carbonyl(triphenylphosphine)rhodium(I),-   (acetylacetonato)dicarbonylrhodium(I),-   carbonylchlorobis(triphenylphosphine)rhodium(I),-   (acetylacetonato)(1,5-cyclooctadiene)rhodium(I),-   rhodium(II) acetate dimer, rhodium(III) acetylacetonate and-   rhodium(II) octanoate dimer.

The amount of the inventively used rhodium catalyst (D) depends on thedesired crosslinking rate and the respective use, and also on economicaspects. The inventive compositions comprise rhodium catalysts (D) inamounts which result in a rhodium content of preferably from 0.05 to 500ppm by weight (=parts by weight per million parts by weight),particularly preferably from 0.5 to 100 ppm by weight, in particularfrom 1 to 50 ppm by weight, in each case based on the total weight ofthe composition.

Apart from the components (A) to (D), the inventive curable compositionscan also contain all other substances which have also previously beenused for producing addition-crosslinkable compositions.

Examples of reinforcing fillers which can be used as component (E) inthe inventive compositions are preferably pyrogenic or precipitatedsilicic acids having BET surface areas of at least 50 m²/g and alsocarbon blacks and activated carbons such as furnace black and acetyleneblack, pyrogenic and precipitated silicic acids having BET surface areasof at least 50 m²/g being preferred.

Said silicic acid fillers can have a hydrophilic character or can berendered hydrophobic by known processes. When hydrophilic fillers aremixed in, it is necessary to add a hydrophobizing agent.

The content of actively reinforcing filler (E) in the inventivecrosslinkable composition is in the range from 0 to 70% by weight,preferably from 0 to 50% by weight.

The inventive silicone rubber composition can optionally comprise, asconstituent (F), other additives at a content of up to 70% by weight,preferably from 0.0001 to 40% by weight. These additives can be, forexample, inactive fillers, resin-like polyorganosiloxanes which aredifferent from the siloxanes (A), (B) and (C), dispersants, solvents,adhesion promoters, coloring agents such as inorganic pigments (forexample cobalt blue) and organic dyes, plasticizers, organic polymers,etc. These include additives such as quartz flour, diatomaceous earth,clays, chalk, lithopone, carbon black, graphite, metal oxides, metalcarbonates, metal sulfates, metal salts of carboxylic acids, metaldusts, fibers such as glass fibers, plastic fibers, plastic powders,metal dusts, dyes, pigments etc. Furthermore, agents to improve heatresistance and flame retarding ability, what are termed heatstabilizers, can be added. Here, all heat stabilizers employed to datein silicone rubbers can be used. Preferably, however, these aretransition metal compounds and carbon black. Examples are cerium oxide,cerium octoate, cerium-siloxane compounds, iron oxide, iron octoate,iron-siloxane compounds, zinc carbonate, manganese carbonate andtitanium oxide.

Furthermore, additives (G) can be present which serve for selectivesetting of the processing time, and crosslinking start temperature andcrosslinking rate of the inventive compositions. These inhibitors andstabilizers are very well known in the field of addition-crosslinkingcompositions. Examples of customary inhibitors are acetylenic alcohols,such as 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol,3,5-dimethyl-1-hexyn-3-ol and 3-methyl-1-dodecyn-3-ol,polymethylvinylcyclosiloxanes, such as1,3,5,7-tetravinyltetramethyltetracyclosiloxane, low-molecular-weightsilicone oils containing methylvinylSiO_(2/2)groups and/orR₂vinylSiO_(1/2) end groups such as divinyltetramethyldisiloxane,tetravinyidimethyldisiloxane, trialkyl cyanurates, alkyl maleates, suchas diallyl maleates, dimethyl maleate and diethyl maleate, alkylfumarates, such as diallyl fumarate and diethyl fumarate, organichydroperoxides, such as cumene hydroperoxide, tert-butyl hydroperoxideand pinane hydroperoxide, organic peroxides, organic sulfoxides, organicamines, diamines and amides, phosphanes and phosphites, nitriles,triazoles, diaziridines and oximes. The effect of these inhibitoradditions (G) depends on their chemical structure such that it must bedetermined individually.

The inhibitor content of the inventive compositions is preferably from 0to 50,000 ppm, particularly preferably from 0 to 1000 ppm, in particularfrom 0 to 100 ppm.

The inventive organopolysiloxane compositions can, if required, bedissolved, dispersed, suspended or emulsified in liquids. The inventivecompositions can, in particular depending on the viscosity of theconstituents and also filler content, be of low viscosity and pourable,have a pasty consistency, be pulverulent or else be conformablehigh-viscosity compositions, as is known can be the case with thecompositions frequently termed in specialist circles RTV-1, RTV-2, LSRand HTV. With respect to the elastomeric properties of the crosslinkedinventive silicone compositions, likewise the entire spectrum iscomprised, starting with extremely soft silicone gels, via rubber-likematerials up to highly crosslinked silicones having a glasslikebehavior.

The invention further relates to a process for preparing the inventiveorganopolysiloxane compositions by mixing the rhodium catalyst (D) witha mixture composed of (A), if appropriate (E) and (F), and (B).

The inventive organopolysiloxane compositions can be prepared by knownprocesses, for example by homogeneous mixing of the individualcomponents. The sequence here may be as desired, but preference is to begiven to homogeneous mixing of the rhodium catalyst (D) with a mixtureof (A), if appropriate (E) and (F), and (B) as the final component. Themixture can also be made up as a two-component system, in a similarmanner to the known platinum-crosslinking mixtures. In this case thefirst component generally comprises (A), (D) and if appropriate (E) and(F) and the second component comprises (B) and if appropriate (A), (E)and (F). However, the two-component system can alternatively be made upin such a manner that the first component comprises (A), (B) and ifappropriate (E) and (F), and the second component consists of (D) and ifappropriate (A), (E) and (F). In the case of the two-component systems,the two components must be mixed before the crosslinking which can beperformed, according to viscosity, either with a stirrer, dissolver,roll or kneader. The two components can be made up in such a manner thatthe components preferably need to be mixed in a ratio of 1:1, but theycan also be made up in such a manner that for 200 parts by weight of onecomponent, 1 part by weight of the other component is present. Allmixing ratios lying between these are also possible. The inventivelyused rhodium catalyst (D) can be incorporated as solid substance or assolution, dissolved in a suitable solvent, or as what is termed amasterbatch, homogeneously mixed with a small amount of (A) or (A) with(E). The mixing, depending on the viscosity of (A), is performed, forexample, using a stirrer, in a dissolver, on a roller or in a kneader.The catalyst (D) can also be encapsulated in an organic thermoplastic orthermoplastic silicone resin.

The inventively used components (A) to (G) can be in each case a singletype of such a component, or else a mixture of at least two differenttypes of such a component.

The inventive compositions which can be crosslinked by addition ofSi-bonded hydrogen to aliphatic multiple bond can be crosslinked underthe same conditions as the previously known compositions which can becrosslinked by hydrosilylation reactions with platinum. Preference isgiven here to temperatures of from 50 to 220° C., particular preferenceto from 120 to 190° C., and to a pressure of from 900 to 1100 hPa.However, alternatively, higher or lower temperatures and pressures canbe employed. The crosslinking can also be carried out photochemicallyusing high-energy radiation, for example visible light of shortwavelengths and UV light, or with a combination of thermal andphotochemical excitation.

The present invention also relates to extrudates and moldings producedby crosslinking the inventive compositions.

The inventive compositions and also the crosslinking products producedtherefrom according to the invention can be used for all purposes forwhich the organopolysiloxane compositions which have also previouslybeen crosslinkable to give elastomers, or elastomers, have been used.This comprises, for example, silicone coating or impregnation of anydesired substrates, production of molded parts, for example in theinjection-molding process, vacuum extrusion process, extrusion process,casting in molds and compression molding, and castings, uses as sealing,embedding or pouring compositions etc. Particular preference is given tomolded parts and extrudates which must have a particularly hightransparency, such as diving masks, pacifiers, spectacle cleaning bathsand desired adhesions and coatings of transparent substrates, such asglass and polycarbonate, food molds, such as baking molds or molds forproducing confectionary products such as chocolate candies; tubes,profiles, seals and damping elements, etc.

The inventive crosslinkable compositions have the advantage that theycan be prepared in a simple process using readily accessible startingmaterials and can thus be prepared economically.

The inventive crosslinkable compositions have the advantage that, asinhibitor-free formulations at 25° C. and ambient pressure, they have agood shelf life and do not crosslink rapidly until at elevatedtemperature.

The inventive silicone compositions have the advantage that they, in thecase of two-component formulation give, after the two components aremixed, a crosslinkable silicone composition whose processabilitypersists over a long period at 25° C. and ambient pressure (extremelylong potlife) and which does not crosslink rapidly until at elevatedtemperature.

The inventive compositions have the further advantage that thecrosslinked silicone rubbers have excellent translucency andtransparency.

The inventive compositions further have the advantage that thecrosslinked silicone rubbers are not yellow or brown colored.

The inventive compositions further have the advantage that thehydrosilylation reaction does not slow down with the length of thereaction time.

The inventive compositions further have the advantage that thehydrosilylation reaction does not change even after relatively longstorage at room temperature (in particular does not slow down).

In the examples described hereinafter, all data on parts andpercentages, unless otherwise stated, are based on weight. Unlessotherwise stated, the examples hereinafter are carried out at a pressureof the ambient atmosphere, that is approximately at 1000 hPa, and atroom temperature, that is at approximately 20° C., or at a temperaturewhich is established when combining the reactants at room temperaturewithout additional heating or cooling.

Hereinafter, all viscosity data are based on a temperature of 25° C.

EXAMPLE 1

A laboratory kneader was charged with 405 parts of avinyldimethylsiloxy-terminated polydimethylsiloxane having a viscosityof 20 Pa·s; this was heated up to 150° C. and admixed with 366 parts ofa hydrophobic pyrogenic silicic acid having a specific BET surface areaof 300 m²/g and a carbon content of 4.2% by weight. This produced ahigh-viscosity composition which was then diluted with 229 parts of theabovementioned polydimethylsiloxane. By kneading under vacuum (10 mbar)at 150° C., volatile constituents were removed in the course of onehour. This composition is termed basic composition 1.

Component A

906 parts of the basic composition 1 were mixed homogeneously undervacuum in the kneader at room temperature with 7 parts of avinyidimethylsiloxy-terminated polydimethylsiloxane having a viscosityof 20 Pa·s and 0.061 parts of bis(triphenylphosphine)carbonylrhodium(I)chloride (this corresponds to 10ppm of rhodium in the total mass of component A), dissolved intetrahydrofuran.

Component B

931 parts of the basic composition 1 were mixed on a roller at atemperature of 25° C. with 55 parts of SiH crosslinker to give ahomogeneous composition, with the SiH crosslinker being atrimethylsiloxy-terminal methyl hydrogen polysiloxane,Me₃Si—(—O—SiH(Me))_(n)—O—SiMe₃, which according to ²⁹Si—NMR has a numberaverage chain length of n=53.

Before the crosslinking, the components A and B were mixed in a ratio of1:1 using a laboratory agitator.

EXAMPLE 2

Similar to Example 1, except that, instead ofbis(triphenylphosphine)carbonylrhodium(I) chloride/tetrahydrofuransolution, 0.029 parts of rhodium(III) acetylacetonate, dissolved indichloromethane, were used.

EXAMPLE 3

Similar to Example 1, except that instead ofbis(triphenylphosphine)carbonylrhodium(I) chloride/tetrahydrofuransolution, 0.021 parts of carbonyltriphenylphosphinerhodium(I)acetylacetonate dissolved in dichioromethane were used.

COMPARATIVE EXAMPLE 1

The procedure described in Example 1 is repeated except that thecatalyst used was 16 ppm of platinum asplatinum-divinyltetramethyldisiloxane complex in vinyl-terminatedpolydimethylsiloxane (commercially available from ABCR GmbH & Co,Germany).

COMPARATIVE EXAMPLE 2

The procedure described in Example 1 is repeated except that thecatalyst used was 16 ppm of platinum asplatinum-divinyltetramethyldisiloxane complex in vinyl-terminatedpolydimethylsiloxane (commercially available from ABCR GmbH & Co,Germany) and 2 parts of ethynylcyclohexanol were used as inhibitor.

EXAMPLE 4

589.4 parts of a vinyldimethylsiloxy-terminated polydimethylsiloxanehaving a Brabender plasticity of 630 mkp equivalent to a mean molar massof approximately 500,000 g/mol were mixed with 252.6 parts by mass of ahydrophobic pyrogenic silicic acid having a BET surface area of 300 m²/gand a carbon content of 3.95% by weight, which were added in portions,for 4 hours in a kneader to give a homogeneous composition.

500 parts of the basic composition 2 thus obtained were mixed on aroller at a temperature of 20° C. with 0.1 part of inhibitor, 7.5 partsof SiH crosslinker and 2 parts of catalyst batch to give a homogeneouscomposition, in which case the inhibitor used was1-ethynyl-1-cyclohexanol, and the SiH crosslinker was a mixed polymer ofdimethylsiloxy and methylhydrogensiloxy and trimethylsiloxy units havinga viscosity of 310 mPa·s at 25° C. and a Si-bonded hydrogen content of0.46% by weight. The catalyst batch is prepared by homogenizing 200parts of the above described basic composition 2 with 1.8 parts ofrhodium(II) octanoate dimer (dissolved in dichloromethane) for 30minutes in a kneader.

COMPARATIVE EXAMPLE 3

The procedure described in Example 4 is repeated except that thecatalyst used was 10 ppm of platinum asplatinum-divinyltetramethyldisiloxane complex in vinyl-terminatedpolydimethylsiloxane (commercially available from ABCR GmbH & Co,Germany) and 0.5 parts of inhibitor (=1-ethynyl-1-cyclohexanol) wereused.

The thermal curing properties of the silicone compositions prepared inExamples 1 to 4 and Comparative Examples 1 to 3 (C1, C2, C3) weremeasured using a Goettfert Elastograph, more precisely 7 hours after theA and B components had been mixed in a ratio of 1:1. Example 4 andComparative Example 3 were measured immediately after mixing.

For quantitative determination of the stability, the formulationsprepared were stored at room temperature (RT), the time (measured indays) for the initial viscosity value to double being determined. Themeasurement results are shown in Table 1.

TABLE 1 Examples 1 2 3 C1 C2 4 C3 a_(T) [° C.] 132 125 118 —* 120 135122 Storage at >10 d >10 d >10 d <<1 d <8 d >10 d <4 d RT —*: Themixture was already crosslinked before the measurement. d: days s:seconds

The kick-off temperature a_(T) was determined using a heating rate of10° C./min. The temperature corresponding to the 4% value of maximumtorque was defined as the kick-off temperature.

The t₅₀ value was determined in accordance with DIN 53529 T3. The timefrom the start of curing to 50% (t₅₀ value) of the maximum torque wasdetermined at 150° C.

For further comparison, crosslinked silicone rubber films were producedfrom the silicone compositions and the mechanical properties weredetermined. The crosslinked silicone rubbers were produced bycrosslinking the mixture of the respective example in a hydraulic pressat a temperature of 170° C. for 10 minutes to give the silicone rubber.The demolded silicone rubber films, of approximately 2 mm or 6 mm inthickness, were subjected to mechanical tests.

The result is shown in Table 2.

TABLE 2 Hardness TS EB [Shore A] [N/mm²] [%] Appearance Example 1 5811.8  570 colorless, transparent Example 2 56 10.4  550 colorless,transparent Example 3 60 11.0  580 colorless, transparent Comparison C1—* —* —* —* Comparison C2 60 10.8  580 slight yellow coloration Example4 37 12.3 1180 colorless, transparent Comparison C3 39 13.0 1100 yellowhue —* Already crosslinked in advance. Hardness: Shore A hardness wasdetermined in accordance with DIN 53505, TS: Tear strength wasdetermined in accordance with DIN 53504-S1 EB: Elongation at break wasdetermined in accordance with DIN 53504-S1 TPR: Tear propagationresistance was determined in accordance with ASTM D 624 RR: Reboundresilience was determined in accordance with DIN 53512

EXAMPLE 5

50.0 g of a vinyldimethylsiloxy-terminated polydimethylsiloxane having aviscosity of 20 Pa·s, and 1.0 g of SiH crosslinker, were homogeneouslymixed using a TYPE RE 162 agitator from Janke & Kunkel IKA-Labortechnikin which case the SiH crosslinker was a mixed polymer of dimethylsiloxyand methylhydrogensiloxy and trimethylsiloxy units having a viscosity of330 mPa·s and a content of Si-bonded hydrogen of 0.46% by weight. Then,3.7 mg of bis(triphenylphosphine)carbonylrhodium(I) chloride (this isequivalent to a content of 10 ppm of rhodium based on the total mass),dissolved in 0.5 ml of methylene chloride, and 60 mg of1-ethynyl-1-cyclohexanol were stirred in at room temperature.

COMPARATIVE EXAMPLE 4

The procedure described in Example 5 is repeated except that, instead ofthe rhodium catalyst, 10 ppm of platinum asplatinum-divinyltetramethyldisiloxane complex in vinyl-terminatedpolydimethylsiloxane (commercially available from ABCR GmbH & Co,Germany) were used.

The thermal curing properties of the silicone compositions prepared inExample 5 and also Comparative Example 4 (C4) were measured using aDynamic Analyzer RDA II, from Rheometrics employing a heat-up curve from30 to 200° C. and a heating rate of 5° C./minute.

For quantitative determination of the shelf life, the formulationsprepared were stored at room temperature (RT), the time (measured indays) for the initial viscosity value to double being determined. Themeasurement results are shown in Table 3.

TABLE 3 Example 5 C4 Kick-off temperature [° C.] 123 105 Storage atRT >20 d <10 d The kick-off temperature was determined using a heatingrate of 5° C./min. d: Days

1. An addition crosslinkable organopolysiloxane composition which does not generate hydrogen gas upon curing, comprising: (A) at least one compound containing aliphatic carbon-carbon multiple bonds, (B) at least one organopolysiloxane containing Si-bonded hydrogen atoms, (C) or, instead of (A) and (B), at least one organopolysiloxane which contains SiC-bonded radicals containing aliphatic carbon-carbon multiple bonds and also contains Si-bonded hydrogen atoms, and (D) at least one rhodium catalyst selected from the group consisting of compounds of the formulae L(X)Rh(PR³ ₃)_(s)  (VI),  and rhodium (II) octanoate dimer  where R³ are each independently hydrogen, —OR⁴, or a monovalent unsubstituted or substituted C₁₋₂₄ hydrocarbon radical, R⁴ are each independently a hydrogen atom or monovalent unsubstituted or sudstituted C₁₋₂₀ hydrocarbon radical, X where present, is a halogen or hydrogen atom, L are each independently CO, acetylacetonate, 0.5 cyclooctadiene, 0.5 norbornadiene or P(R³)₃, and s is 0 to
 3. 2. The organopolysiloxane composition of claim 1, wherein at least one rhodium compound is selected from the group consisting of (acetylacetonatocarbonyl)(triphenylphosphine)rhodium(I), carbonylchlorobis(triphenylphosphine)rhodium(I), (acetylacetonato)(1,5-cyclooctadiene)rhodium(I), rhodium(II) octanoate dimer.
 3. The organopolysiloxane composition of claim 1, wherein a heat stabilizer is present as a constituent F.
 4. The organopolysiloxane composition as claimed in claim 3, further comprising at least one heat stabilizer selected from the group consisting of cerium oxide, cerium octoate, cerium-siloxane compounds, iron oxide, iron octoate, iron-siloxane compounds, zinc carbonate, manganese carbonate and titanium oxide.
 5. A process for preparing an organopolysiloxane composition of claim 1, comprising mixing a rhodium catalyst (D) with a mixture comprising (A), optionally filler (E), heat stabilizer (F), and (B).
 6. The process of claim 5, wherein said organopolysiloxane composition comprises two components, a first component comprising (A), (D), and optionally (E) and optionally (F), and a second component comprising (B), optionally (A), optionally (E), and optionally (F).
 7. The process of claim 1, wherein said organopolysiloxane composition comprises two components, a first component comprising (A), (B), optionally (E) and optionally (F), and a second component comprising (D), optionally (A), optionally (E), and optionally (F).
 8. A molding or extrudate prepared by curing the organopolysiloxane composition of claim
 1. 9. A molding or extrudate prepared by curing the B organopolysiloxane composition of claim
 2. 10. A molding or extrudate prepared by curing the B organopolysiloxane composition of claim
 3. 11. A food mold which comprises a molding or extrudate prepared by curing an organopolvsiloxane composition which does not generate hydrogen gas upon curing, comprising: (A) at least one compound containing aliphatic carbon-carbon multiple bonds, (B) at least one organopolvsiloxane containing Si-bonded hydrogen atoms, (C) or, instead of (A) and (B), at least one organopolysiloxane which contains SiC-bonded radicals containing aliphatic carbon-carbon multiple bonds and also contains Si-bonded hydrogen atoms, and (D) at least one rhodium catalyst selected from the group consisting of compounds of the formulae L(X)Rh(PR³ ₃)^(s)  (VI),  and rhodium (II) octanoate dimer  where R³ are each independently hydrogen, —OR⁴, or a monovalent unsubstituted or substituted C₁₋₂₄ hydrocarbon radical, R⁴ are each independently a hydrogen atom or a monovalent unsubstituted or substituted C₁₋₂₀ hydrocarbon radical, X Where present, is a halogen or hydrogen atom, L are each independently CO, acetylacetonate, 0.5 cyclooctadiene, 0.5 norbornadiene or P(R³)₃, and s is 0 to
 3. 12. The molding or extrudate of claim 8, which is colorless and transparent.
 13. An addition crosslinkable organopolysiloxane composition which does not generate hydrogen gas upon curing, comprising: (A) at least one compound containing aliphatic carbon-carbon multiple bonds, (B) at least one organopolysiloxane containing Si-bonded hydrogen atoms, (C) or, instead of (A) and (B), at least one organopolysiloxane which contains SiC-bonded radicals containing aliphatic carbon-carbon multiple bonds and also contains Si-bonded hydrogen atoms, and (D) at least one rhodium catalyst selected from the group consisting of compounds of the formulae L(X)Rh(PR³ ₃)_(s)  (VI),  and rhodium (II) octanoate dimer  where R³ are each independently hydrogen, —OR⁴, or a monovalent unsubstituted or substituted C₁₋₂₄ hydrocarbon radical, R⁴ are each independently a hydrogen atom or a monovalent unsubstituted or substituted C₁₋₂₀ hydrocarbon radical, X Where present, is a halogen or hydrogen atom, L are each independently CO, acetylacetonate, 0.5 cyclooctadiene, 0.5 norbornadiene or P(R³)₃, and s is 0 to
 3. wherein at least one compound (A) is a vinyldimethylsilyl-terminated polydiorganosiloxane wherein said organo groups are selected from the group consisting of alkyl groups and phenyl groups.
 14. The composition of claim 13, wherein at least one compound (A) is a vinyldimethylsilyl-terminated polydimethylsiloxane.
 15. The composition of claim 11, wherein at least one catalyst is selected from the group consisting of bis[triphenylphosphine]carbonylrhodium (I) chloride, carbonyl[triphenylphosphine]rhodium acetylacetonate, acetylacetonato (1,5-cyclooctadiene)rhodium (I), and (acetylacetonato)dicarbonylrhodium (I).
 16. The composition of claim 13, wherein at least one catalyst is selected from the group consisting of bis[triphenylphosphine]carbonylrhodium (I) chloride, carbonyl[triphenylphosphine]rhodium acetylacetonate, acetylacetonato (1,5-cyclooctadiene)rhodium (I), and (acetylacetonato)dicarbonylrhodium (I).
 17. The organopolysiloxane composition as claimed in claim 13, further comprising at least one heat stabilizer selected from the group consisting of cerium oxide, cerium octoate, cerium-siloxane compounds, iron oxide, iron octoate, iron-siloxane compounds, zinc carbonate, manganese carbonate and titanium oxide.
 18. The organopolysiloxane composition as claimed in claim 15, further comprising at least one heat stabilizer selected from the group consisting of cerium oxide, cerium octoate, cerium-siloxane compounds, iron oxide, iron octoate, iron-siloxane compounds, zinc carbonate, manganese carbonate and titanium oxide.
 19. The organopolysiloxane composition as claimed in claim 16, further comprising at least one heat stabilizer selected from the group consisting of cerium oxide, cerium octoate, cerium-siloxane compounds, iron oxide, iron octoate, iron-siloxane compounds, zinc carbonate, manganese carbonate and titanium oxide. 